The GDAP1 p.Glu222Lys Variant-Weak Pathogenic Effect, Cumulative Effect of Weak Sequence Variants, or Synergy of Both Factors?

Charcot−Marie−Tooth disorders (CMT) represent a highly heterogeneous group of diseases of the peripheral nervous system in which more than 100 genes are involved. In some CMT patients, a few weak sequence variants toward other CMT genes are detected instead of one leading CMT mutation. Thus, the presence of a few variants in different CMT-associated genes raises the question concerning the pathogenic status of one of them. In this study, we aimed to analyze the pathogenic effect of c.664G>A, p.Glu222Lys variant in the GDAP1 gene, whose mutations are known to be causative for CMT type 4A (CMT4A). Due to low penetrance and a rare occurrence limited to five patients from two Polish families affected by the CMT phenotype, there is doubt as to whether we are dealing with real pathogenic mutation. Thus, we aimed to study the pathogenic effect of the c.664G>A, p.Glu222Lys variant in its natural environment, i.e., the neuronal SH-SY5Y cell line. Additionally, we have checked the pathogenic status of p.Glu222Lys in the broader context of the whole exome. We also have analyzed the impact of GDAP1 gene mutations on the morphology of the transfected cells. Despite the use of several tests to determine the pathogenicity of the p.Glu222Lys variant, we cannot point to one that would definitively solve the problem of pathogenicity.

The genetic landscape of axonal neuropathies in the middle-aged and elderly: Focus on MME.

OBJECTIVE: To test the hypothesis that monogenic neuropathies such as Charcot-Marie-Tooth disease (CMT) contribute to frequent but often unexplained neuropathies in the elderly, we performed genetic analysis of 230 patients with unexplained axonal neuropathies and disease onset ≥35 years. METHODS: We recruited patients, collected clinical data, and conducted whole-exome sequencing (WES; n = 126) and MME single-gene sequencing (n = 104). We further queried WES repositories for MME variants and measured blood levels of the MME-encoded protein neprilysin. RESULTS: In the WES cohort, the overall detection rate for assumed disease-causing variants in genes for CMT or other conditions associated with neuropathies was 18.3% (familial cases 26.4%, apparently sporadic cases 12.3%). MME was most frequently involved and accounted for 34.8% of genetically solved cases. The relevance of MME for late-onset neuropathies was further supported by detection of a comparable proportion of cases in an independent patient sample, preponderance of MME variants among patients compared to population frequencies, retrieval of additional late-onset neuropathy patients with MME variants from WES repositories, and low neprilysin levels in patients' blood samples. Transmission of MME variants was often consistent with an incompletely penetrant autosomal-dominant trait and less frequently with autosomal-recessive inheritance. CONCLUSIONS: A detectable fraction of unexplained late-onset axonal neuropathies is genetically determined, by variants in either CMT genes or genes involved in other conditions that affect the peripheral nerves and can mimic a CMT phenotype. MME variants can act as completely penetrant recessive alleles but also confer dominantly inherited susceptibility to axonal neuropathies in an aging population.

Clinical, electrophysiological, and molecular findings in early onset hereditary neuropathy with liability to pressure palsy.

INTRODUCTION: The first episode of hereditary neuropathy with liability to pressure palsy (HNPP) in childhood is rare. METHODS: We analyzed retrospectively the data of 7 patients with a deletion in PMP22 and onset of symptoms before age 18 years. Direct sequencing of the LITAF (lipopolysaccharide-induced tumor necrosis factor) gene was performed in patients and family members. RESULTS: Clinical presentations varied from mononeuropathies to brachial plexopathy, with recurrent episodes in 4 patients. Electrophysiological abnormalities characteristic for HNNP were found in most subjects. Analysis of the LITAF gene revealed an Ile92Val polymorphism in 6 of 7 (86%) probands and 5 of 7 (83%) family members, over 4 times greater frequency than in the general population. CONCLUSIONS: Clinical suspicion of HNPP even when nerve conduction study results do not fulfill HNPP criteria should indicate genetic testing. In our patients, early-onset HNPP was associated frequently with isoleucine92valine LITAF polymorphism.

Charcot-Marie-Tooth type 1C disease coexisting with progressive multiple sclerosis: a study of an overlapping syndrome.

Charcot-Marie-Tooth type 1C disease (CMT1C) is a rare form of hereditary demyelinating neuropathy caused by mutations in the LITAF (lipopolysaccharide-induced tumor necrosis factor-) gene. CMT1C disease was mapped to chromosome 16p12-p 13.3. To date only a few mutations in the LITAF gene have been reported. Due to a small group of CMT1C reported patients, the phenotype of CMT1C is poorly characterized. CMT1C disease is a pure demyelinating neuropathy limited to the peripheral nervous system with a mild clinical course, manifesting without any additional symptoms. To the best of our knowledge, in this study, for the first time we present a three generational CMT1C family in which in the proband, CMT1C disease coexists with central demyelination fulfilling criteria of primary progressive multiple sclerosis (PPMS). The coexistence of PPMS and CMT1C in one family may not result from a common pathogenetic trait, however only in the proband with central demyelination and CMT1C we have detected a -308G>A sequence variant in the promoter of the TNF-α gene.

Is a novel I214M substitution in the NEFL gene a cause of Charcot-Marie-Tooth disease? Functional analysis using cell culture models.

Recent studies have shown that mutations in neurofilament light subunit gene (NEFL) cause Charcot-Marie-Tooth (CMT) disease. Since the first description of the Gln333Pro mutation in the NEFL gene, 10 pathogenic mutations in the NEFL gene have been reported in patients affected with CMT disease. We report a novel I214M amino acid substitution in the NEFL gene in two unrelated patients affected with CMT. Because the I214M amino acid substitution in the NEFL protein was not detected in a CMT affected brother of the proband, its pathogenic effect became unclear. In order to determine whether this amino acid substitution is a benign polymorphism or causative of the disease, we performed a functional analysis of the mutant I214M neurofilament protein (NFL). Transfections of the mutant protein in cultured cells revealed an increased tendency to form highly compacted filamentous structures but no other alterations of neurofilament assembly or transport were observed. Furthermore, the sibling of one of the patients was also affected with CMT but did not have the I214M substitution. These data suggest that this I214M substitution in the NEFL gene was not a direct cause of the disease but could be a polymorphism or possibly a modifier of the CMT phenotype.

[Genetic investigations in facioscapulohumeral muscular dystrophy: a preliminary report]. / Badania genetyczne w dystrofii twarzowo-lopatkowo-ramieniowej--doniesienie wstepne.

Facioscapulohumeral muscular dystrophy (FSHD) is a primary muscle disorder with autosomal dominant inheritance. FSHD was mapped to chromosome 4 locus q35, but the gene is not yet known. It is characterised by progressive, often asymmetric, selective muscular weakness and great clinical variability. The aim of the study was to analyze 62 FSHD cases from 44 Polish families in which the diagnosis was confirmed by DNA analyses. FSHD diagnosis was based on the clinical findings and standardized investigations confirming primary muscular involvement (EMG, muscle biopsy). DNA analysis was based on EcoRI/BlnI restriction enzyme digestion followed by hybridization with P13E-11 molecular probe. In our material, we have found a relatively large percentage (41%) of big deletions (EcoRI/BlnI fragment of 10-15 kb [kilo bases]), which in the majority of cases (67%) was present in isolated cases. In 10 families (23%) the phenotype was assessed as severe. These are cases with the onset before the age of 10 and fast progression. "Middle sized" deletions (EcoRI/BlnI fragment of 16-29 kb) were prevalent in familial cases and present in 57% of families. "Small" deletion was found in one family (EcoRI/BlnI fragment of 30 kb). Somatic mosaicism was confirmed in one case. De novo mutations were shown in 11% of the examined families. The results of this study indicate that the bigger the deletion, the more severe the FSHD course, however there are some exceptions. A similar relationship has been shown by previous research. Molecular analyses are particularly important in atypical and sporadic cases. It is the first genetic presentation of a group of patients' with this kind of dystrophy in the Polish population.

[Charcot-Marie Tooth type X (CMTX) disease: clinical and genetic characteristics of eleven patients]. / Choroba Charcot-Marie-Tooth typu X--charakterystyka kliniczno-genetyczna jedenastu chorych.

Charcot-Marie-Tooth type X disease (CMTX) is the second most frequent inherited neuropathy, after CMT1A type associated with 17p11.2-p12 duplication. CMTX is inherited as X dominant trait and is caused by point mutations in Cx32 gene. In the study the first Polish group of 11 patients with CMTX from 4 families is presented. The following four mutations were found in Cx32 gene: Gly110Asp, Val 152 Asp, Arg 183 His and Glu 208 Gly. CMTX is characterized by X dominant trait of inheritance, a mild clinical course in affected females and slowly progressive atrophy and weakness of distal limb muscles. Both electrophysiological and sural nerve biopsy studies show axonal changes with secondary demyelination.